Vital signs of a person, for example the heart rate, the respiration rate or the blood oxygen saturation, serve as indicators of the current state of a person and as powerful predictors of serious medical events. For this reason, vital signs are extensively monitored in inpatient and outpatient care settings, at home or in further health, leisure and fitness settings.
WO 2012/140531 A1 discloses a respiratory motion detection apparatus for detecting the respiratory motion of a person. This detection apparatus detects electromagnetic radiation emitted and/or reflected by a person wherein this electromagnetic radiation comprises a continuous or discrete characteristic motion signal related to the respiratory rate of the person and other motion artifacts related to the movement of the person or related to ambient conditions. This apparatus increases the reliability of the respiratory rate measurement by taking into account data processing means adapted to separate the respiratory rate signal from overall disturbances by taking into account a predefined frequency band, common predefined direction or an expected amplitude band and/or amplitude profile to distinguish the different signals.
Non-invasive respiratory rate measurements can be accomplished optically by use of a stationary video camera. A video camera captures the breathing movements of a patient's chest in a stream of images. The breathing movements lead to a temporal modulation of certain image features, wherein the frequency of the modulation corresponds to the respiratory rate of the patient monitored. Examples of such image features are the average amplitude in a spatial region of interest located around the patient's chest, or the location of the maximum of the spatial cross correlation of the region of interest in subsequent images. The quality and the reliability of the obtained vital sign information are largely influenced by the quality of the input image data influenced by an appropriate selection of the image contrast and the selected region of interest.
Camera-based respiration monitoring is based on detecting subtle respiration motion in the selected region of interest (ROI) in the chest/belly area. In real-life use scenarios, a static noise present in an image (including ROI) can be registered, amplified and (falsely) recognized as a respiratory signal. This might happen in cases when only the ROI is analyzed, as well as when a whole image is divided into spatial blocks, which are analyzed separately. Certainly, the noise might be registered as respiratory signal, if a final reconstructed signal is used to evaluate its validity, because in this case a differentiation of noise from breathing is done based on an amplitude and/or frequency of the final 1D signal.
US 2010/130873 A1 discloses a radar-based physiological motion sensor. Doppler-shifted signals can be extracted from the signals received by the sensor. The Doppler-shifted signals can be digitized and processed subsequently to extract information related to the cardiopulmonary motion in one or more subjects. The information can include respiratory rates, heart rates, waveforms due to respiratory and cardiac activity, direction of arrival, abnormal or paradoxical breathing, etc. In various embodiments, the extracted information can be displayed on a display.